RiiConnect24 allows you to send messages to other Wiis again, as long as both Wiis are connected to our service. Many games and apps rely on this feature to send data to other Wiis, so you can send Miis through the Mii Channel or send ghost data or friend rankings with Mario Kart Wii, for example. You can also send messages to people via email or phone, which is powered by SendGrid. To exchange messages with a phone, your phone carrier must have a SMS to email gateway. Here's a list of them.
To see stats of which games currently allow you to send messages to your friends' Wii Message Boards, click here.